When high-speed raindrops collide with the coatings of the fuselage skin structure, such as the radome and the leading edge of the tail wing of a supersonic aircraft, the performance of the coatings is significantly reduced. This poses a potential hazard to the flight safety of the aircraft. To explore the mechanism of rain erosion damage to coatings and establish a criterion for rain erosion damage, this paper evaluates the rain erosion damage behavior of samples coated with different types and thicknesses of aviation polyurethane coatings at various impact velocities. The evaluation is based on a single jet impact test platform built with a single-stage light gas gun. The test results show that as the raindrop impact velocity increases continuously, the impact force on the sample gradually increases. This results in an increasing trend in the damaged area and volume. The typical damage morphology of the sample consists of annular damage, with an undamaged area in the center. As the damage intensifies, a circular peeling damage gradually forms. Compared with mechanical parameters such as hardness and modulus, the effect of surface roughness on the rain erosion damage of the coating is more pronounced. When the primer thickness is kept constant, the rain erosion damage area decreases with increasing topcoat thickness. Conversely, when the topcoat thickness is kept constant, the damage area increases as the primer thickness increases from 100 μm to 150 μm. However, when the primer thickness exceeds 250 μm, the rain erosion damage area decreases. This phenomenon is attributed to the reduction of the reflection and transmission effects of the stress wave when the primer thickness exceeds the critical protective thickness.